In the past, colored smoke formulations have employed the use of mixtures containing a fuel, an oxidizer, and a dye. The principle behind the use of such formulations lies in the reaction between the fuel and oxidizer, and the accompanying release of a large amount of energy during such reaction. The latter exothermic reaction releases the energy contained in the bonds of the highly structured fuel molecule as heat. This causes the dye component of the formulation to undergo phase transitions from a solid to a liquid and ultimately to a vapor. If the temperature of the reaction is too high degradation of the dye will result.
Generally, the dye exists as a solid crystal at standard temperature and pressure. When heat from the cited reaction is applied to the solid crystal, dislocations of the molecule occur in the crystalline lattice. As molecules of the dye become detached from the central lattice, a liquid is formed. As more heat energy is applied, the individual molecules of the dye begin to move faster and faster. The molecules, as a result, translate through space, rotating about the axes of the dye structure, and vibrate in many complex modes. The latter molecular activity is responsible for the transition of the liquid phase to the vapor phase.
It is to be noted that the individual molecules of the dyes are subject to degradation at elevated temperatures. If the molecular structure of the dyes are subject to forces and energies which, if great enough, cause cleavage of the bonds of the molecule, changes in color occur or loss of color properties are likely. Therefore, a dye material is sought which transforms from the solid to the vapor phase with little or no intermediate liquid phase. This enhances the likelihood of the dye escaping in the vapor phase to the atmosphere from the solid matrix made of fuel, oxidizer, and dye. Thus, dyes are sought for the composition which have the property of sublimation at increased temperatures and normal pressures.
Another problem in the art is the production of a solid residue as the smoke-producing composition burns. This contributes to the formation of waste products such as slag and solid clinkers. When such solid materials accumulate in the core of the munition, they prevent the generated gases from escaping. As a result, deflagration can occur which can cause injury, or result in a limited release of colored smoke. Further, the formation of slag increases the decomposition of the dye vapor and may lead to a deterioration of color. It has been found that only a small number of dye materials are suitable for use in the formulations of the art because of the slag or clinker presence.
What is needed in the art is a component of the formulation which will absorb excess energy of the thermally decomposing fuel. Also, what is needed is a compound having a high vapor pressure which will aid in purging the core of excess slag and solid clinkers.